It is known to use a frequency tracking feedback loop to attain frequency lock of a received radio frequency (RF) signal in a satellite radio.
Referring to prior art FIG. 1, one such satellite radio has a conventional frequency tracking feedback loop (1) that includes a frequency shifter CORDIC (3), a matched filter (4), and a decimate by 2 block (5). An input/output (I/O) signal received from the analog-to-digital converter (A/D) of the satellite radio is input in to the frequency shifter CORDIC (3) and is subsequently is electrically transmitted to downstream to the matched filter (4) and the decimate by 2 (5) blocks to electrically feed the symbol demodulation block (6). The electrical signal that is output from the decimate by 2 block (5) is electrically transmitted back to the frequency shifter CORDIC (3) through a feedback loop that includes a Costas Phase Error block (7) and a loop filter block (8). This frequency tracking feedback loop (1) works well in an open land environment where strong satellite signals are broadcast and received by the satellite receiver that are relatively free from obstructions, such as trees and road tunnels underlying road overpasses. However, should the vehicle travel through a portion of the land environment that contains a thick canopy of trees or an extended road tunnel, a weak satellite signal condition may manifest as a result of these obstructions such that the tracking mode frequency loop (1) may not effectively track, or attain frequency lock on a received satellite radio frequency (RF) signal of the broadcasted satellite RF signal. When the frequency tracking feedback loop does not effectively track the received satellite RF signal, a user of the satellite radio, or receiver may experience an undesired loss of received RF signal reception so that a defective listenable audio stream may occur when the vehicle movingly travels through these types of obstructions.
Thus, what is needed is a satellite receiver that has an improved tracking mode feedback loop that allows robust operating performance in weak satellite signal conditions by determining an independent frequency estimate that is a function of data information derived from a preamble of the received satellite RF signal that is used by the satellite receiver to electrically steer the tracking mode frequency loop in a direction during the weak satellite signal condition towards a predetermined tracking range of the tracking mode electronic circuitry so that the tracking mode frequency loop obtains frequency lock of the received satellite RF signal and a quality listenable audio stream for the user is effectively maintained.